Sorry I failed to follow up on this thread in a timely fashion. I try to help where I can, but it can be difficult to follow it all and make sure I reply to everything.
The driver you found is the correct one, and it looks like you loaded it correctly too.
You probably just need to use "reconnect" in the EFI Shell in order to disconnect our FAT filesystem driver from the SCT volume and connect the FAT filesystem driver which you installed (which has a higher driver version number, so it should be preferred to our driver)... Then you should have long filename support on the SCT volume. There is some trickery required in order to obtain the correct handle ID(s) for the "reconnect" command, or you can try "reconnect -r", which will take a while longer to run. You need to ensure that the EFI Shell's current working directory is not on the filesystem that you want to reconnect.
It sounds like you're making good progress with OVMF+qemu anyway, so I just post the above for the sake of completeness, and just in case you find yourself stuck and looking again for another way forward. Sorry once again that I missed responding to your post.
Cheers,
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Darius